A new equation of state for homo-polymers in dissipative particle dynamics.

A chain-revised Groot-Warren equation of state (crGW-EOS) was developed and tested to describe systems of homo-oligomeric chains in the framework of dissipative particle dynamics (DPD). First, thermodynamic perturbation theory is applied to introduce correction terms that account for the reduction in pressure with an increasing number of bonds at constant bead number density. Then, this EOS is modified by introducing a set of switching functions that yields an accurate second virial coefficient in the low-density limit.

Quantum confinement effects on electronic photomobilities at nanostructured semiconductor surfaces: Si(111) without and with adsorbed Ag clusters.

The conductivity of holes and electrons photoexcited in Si slabs is affected by the slab thickness and by adsorbates. The mobilities of those charged carriers depend on how many layers compose the slab, and this has important scientific and technical consequences for the understanding of photovoltaic materials. A previously developed general computational procedure combining density matrix and electronic band structure treatments has been applied to extensive calculations of mobilities of photoexcited electrons and holes at Si(111) nanostructured surfaces with varying slab thickness and for varying photon energies, to investigate the expected change in mobility magnitudes as the slab thickness is increased.

Photoconductivities from band states and a dissipative electron dynamics: Si(111) without and with adsorbed Ag clusters.

A new general computational procedure is presented to obtain photoconductivities starting from atomic structures, combining ab initio electronic energy band states with populations from density matrix theory, and implemented for a specific set of materials based on Si crystalline slabs and their nanostructured surfaces without and with adsorbed Ag clusters. The procedure accounts for charge mobility in semiconductors in photoexcited states, and specifically electron and hole photomobilities at Si(111) surfaces with and without adsorbed Ag clusters using ab initio energy bands and orbitals generated from a generalized gradient functional, however with excited energy levels modified to provide correct bandgaps. Photoexcited state populations for each band and carrier type were generated using steady state solution of a reduced density matrix which includes dissipative medium effects.

Photoinduced electron transfer at a Si(111) nanostructured surface: effect of varying light wavelength, temperature, and structural parameters.

We treat electronic dynamics at surfaces of nanostructured semiconductors induced by absorption of visible light using reduced density matrices and properties obtained from ab initio electronic structure calculations, to focus on two non-adiabatic phenomena: (a) how active electrons interacting non-adiabatically with atoms at the surface undergo electronic transitions and (b) how active electrons interacting by exchanging energy with excitons in the medium undergo a dissipative non-adiabatic dynamics. We test the effects on charge separation from varying oscillator strengths, non-adiabatic momentum couplings, the rates of relaxation of excited states coupled to the medium, temperature, and light wavelength. Varying the oscillator strength displays the interplay between competing relaxation and charge transfer dynamics.